1. Field of the Invention
The present invention relates generally to filter apparatus having replaceable filter elements and, more particularly, but not by way of limitation, to apparatus for filtering liquid-gas mixtures.
2. Brief Description of the Prior Art
Filters are used for a variety of purposes in industry to remove particulate matter from various fluids. For example, in a process for synthesizing a chemical product from given feed stocks, it may be necessary to filter the feed stocks entering a reactor in which the synthesis is carried out, the product from the reactor, or both. Filters are also often used in processes in which a fluid is continuously circulated to carry out some purpose; for example, cleaning, and then reused after removal of contaminants introduced by the use to which the fluid is put.
To meet the varying purposes for which filters are used, a variety of types of filter units have been developed. In particular, it is known to construct a filter unit to comprise a tank having an inlet portion and an outlet portion that are separated by one or more filter cartridges that can be replaced by opening the tank to remove the cartridges and replace them with other cartridges. In some cases, the cartridge is designed to be discarded after it has become clogged while, in other cases, the cartridge is designed to be cleaned and replaced in the tank. In either of these cases, the cartridge may include a filter element and an element holder so that the filter element can be removed and discarded or removed and cleaned.
While filter units which include removable cartridges can often provide economical solutions to particular filtration problems, difficulties have existed with prior art filter units of this type. In particular, difficulties have arisen with replaceable cartridge type filter units which must filter a liquid-gas mixture in operation. Because of the tendency of the liquid and gas to separate, the outlet of the tank must be placed near the upper end thereof in order that the gases entering the tank can escape therefrom. On the other hand, liquids entering the tank must rise to the level of the outlet to issue from the tank. These requirements can conflict to cause problems in the replacement of filter elements in the apparatus. If the outlet is high enough on the tank to permit any gas entering the tank to escape therefrom, liquid entering the tank will rise to a correspondingly high level and remain at such level when fluid flow into the tank is discontinued to permit replacement of filter elements. The result is that a high placement of the outlet tends to cause submergence of filter cartridges in the filter apparatus so that the tank must be at least partially drained to replace the cartridges. Thus, a high placement of the outlet with respect to the cartridges can result in excessive down time of a process using a filter apparatus when filter elements must be replaced and, in addition, can result in an undesirable loss of liquid from a system in which the filter apparatus is used. Returning the liquid to the system can, in some cases, give rise to unwanted contamination of chemicals which are involved in the process in which the filter apparatus is used. On the other hand, placement of the outlet low on the tank to prevent submergence of the filter cartridges can result in trapping of gases in the upper end of the tank with various attendant problems; for example, a pressure build-up in the tank that can rupture seals or give rise to excessive power requirements to force a fluid through the tank.
Other problems can also arise with filter apparatus designed to filter liquid-gas mixtures. In some cases, tank outlets have been placed on the cover of the tank that is removed to replace the cartridges in order to prevent a build-up of gas pressure in the tank. When this occurs, not only can a cartridge submergence problem arise but it becomes necessary to disconnect conduits connected to the outlet in order to remove the cover. Such discontinuation will increase an already undesireably long down time, stemming from the need to drain the tank for filter replacement when the outlet is so mounted, for a process in which the apparatus is used.
In general, then, prior art filter apparatus have not provided filter users with filtration capabilities that are desired when the process in which the filter apparatus is used requires that a liquid-gas mixture be filtered. In the past, users of filter units have had to accept problems related to gaseous pressure build-up in such units or, in avoiding these problems, have had to accept excessive process down times in periodically replacing filter cartridges in the units. The present invention provides a versatile filter apparatus which is capable of filtering a liquid-gas mixture without gaseous pressure build-up in the apparatus and, at the same time, has a rapid filter element replacement capability.